This is unfortunate, but quite common. If you accept credit cards online, you're at risk. The specific kind of fraudulent behavior you see will depend on severa

This is unfortunate, but quite common. If you accept credit cards online, you're at risk. The specific kind of fraudulent behavior you see will depend on several factors (the nature of your business; whether you enable transfer from users to just yourself, or whether you push money from one user to another.) Credit card companies will, some time later, probably notice the fraud. At that point, you'll get a chargeback: you'll have to pay back the money you charged in addition to a fixed penalty per fraudulent charge (usually $15.) Especially if you're enabling a marketplace, like gittip does, these fees can be devastating. Regardless, if chargebacks become too common, your merchant account may be suspended. I've written some about my company's experiences with fraud, if it's of interest: http://davepeck.org/2011/11/17/fraudsters-gonna-fraud/ http://davepeck.org/2011/11/17/fraudsters-gonna-fraud/ http://davepeck.org/2011/12/01/dealing-with-credit-card-fraud/ http://davepeck.org/2011/12/01/dealing-with-credit-card-frau...